CODEWITHSUNDEEP
djangodjango-queryset
HTF
HTF

Reputation: 7260

Django: minimize database hits with QuerSets

I've got this custom admin command to remove some old records. QuerySets are lazy so I was wondering if there is a way to optimize this code because at the moment there are four hits to database in --dry-run mode: 

class Command(BaseCommand):

    def add_arguments(self, parser):
        parser.add_argument('--dry-run', action='store_true')

    def handle(self, *args, **options):
        threshold = timezone.now() - timezone.timedelta(5)
        try:
            if options['dry_run']:
                queryset = Mointor.objects.filter(created__lt=threshold)
                if queryset.exists():
                    msg = f'{queryset.count()} record(s) will be deleted, from {queryset.first().created} to {queryset.last().created}'
                else:
                    msg = 'No records to delete'
            else:          
                Monitor.objects.filter(created__lt=threshold).delete()
                msg = 'OK'
        except Exception as e:
            raise CommandError(e)

        self.stdout.write(msg)

Upvotes: 1

Views: 45

Answers (1)

Alexandr Tatarinov
Alexandr Tatarinov

Reputation: 4034

You can firsty do count = queryset.count() and then use it as if condition and insert inside string. So you will get rid of exists query. Also to find date range, you can use aggregate with Min and Max, so you have saved another query here. But as for me, it is not really a problem. Remember, don't optimize prematurely unless you are sure you have a performance issue.

Upvotes: 2

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